[PATCH V40 12/29] x86: Lock down IO port access when the kernel is locked down

[Kai-Heng Feng]

Hi Matthew,

On Tue, Aug 20, 2019 at 8:20 AM Matthew Garrett
<matthewgarrett at google.com> wrote:
>
> From: Matthew Garrett <mjg59 at srcf.ucam.org>
>
> IO port access would permit users to gain access to PCI configuration
> registers, which in turn (on a lot of hardware) give access to MMIO
> register space. This would potentially permit root to trigger arbitrary
> DMA, so lock it down by default.
>
> This also implicitly locks down the KDADDIO, KDDELIO, KDENABIO and
> KDDISABIO console ioctls.
>
> Signed-off-by: Matthew Garrett <mjg59 at google.com>
> Signed-off-by: David Howells <dhowells at redhat.com>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> cc: x86 at kernel.org
> Signed-off-by: James Morris <jmorris at namei.org>

This patch breaks ioperm() usage from userspace programs with CAP_SYS_RAWIO cap.

I wonder if it's possible to revert this commit?

Kai-Heng

> ---
>  arch/x86/kernel/ioport.c     | 7 +++++--
>  include/linux/security.h     | 1 +
>  security/lockdown/lockdown.c | 1 +
>  3 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
> index 0fe1c8782208..61a89d3c0382 100644
> --- a/arch/x86/kernel/ioport.c
> +++ b/arch/x86/kernel/ioport.c
> @@ -11,6 +11,7 @@
>  #include <linux/errno.h>
>  #include <linux/types.h>
>  #include <linux/ioport.h>
> +#include <linux/security.h>
>  #include <linux/smp.h>
>  #include <linux/stddef.h>
>  #include <linux/slab.h>
> @@ -31,7 +32,8 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
>
>         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
>                 return -EINVAL;
> -       if (turn_on && !capable(CAP_SYS_RAWIO))
> +       if (turn_on && (!capable(CAP_SYS_RAWIO) ||
> +                       security_locked_down(LOCKDOWN_IOPORT)))
>                 return -EPERM;
>
>         /*
> @@ -126,7 +128,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, level)
>                 return -EINVAL;
>         /* Trying to gain more privileges? */
>         if (level > old) {
> -               if (!capable(CAP_SYS_RAWIO))
> +               if (!capable(CAP_SYS_RAWIO) ||
> +                   security_locked_down(LOCKDOWN_IOPORT))
>                         return -EPERM;
>         }
>         regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 2b763f0ee352..cd93fa5d3c6d 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -108,6 +108,7 @@ enum lockdown_reason {
>         LOCKDOWN_KEXEC,
>         LOCKDOWN_HIBERNATION,
>         LOCKDOWN_PCI_ACCESS,
> +       LOCKDOWN_IOPORT,
>         LOCKDOWN_INTEGRITY_MAX,
>         LOCKDOWN_CONFIDENTIALITY_MAX,
>  };
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index 410e90eda848..8b7d65dbb086 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -23,6 +23,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>         [LOCKDOWN_KEXEC] = "kexec of unsigned images",
>         [LOCKDOWN_HIBERNATION] = "hibernation",
>         [LOCKDOWN_PCI_ACCESS] = "direct PCI access",
> +       [LOCKDOWN_IOPORT] = "raw io port access",
>         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
>         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
>  };
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>